The present invention relates to a process for shrink-fit locking a cylindrical ceramic part into a flange made of a ferrous material, in particular a ceramic piston in a steel holding means connected to a power drive in conveyance facilities for liquid and gaseous media, by introducing part of the ceramic component into a bore in the heated flange and cooling the same to room temperature.
Ceramic-metal composite components are finding increasing application in the machine construction industry, especially in internal combustion engines or pumping facilities that run at very high speeds. In such cases one makes use of the advantageous properties of the ceramic material viz., the resistance to high temperatures and temperature changes and/or the wear resistance. In the field of high pressure pumping in particular ceramic pistons of various diameters find application for densifying fluids for cleaning operations. In the case of such ceramic pistons the foot must be connected to a flange which drives the piston to effect its purpose. The flange in most cases is made of a ferrous material and the connection is made via bolting, adhesive bonding or shrink-fitting. Because of the hgh frequency of the backwards and forwards movement of the piston, a strong tensile force acts on the piston in the direction of its longitudinal axis; in even small pistons of e.g. 20 mm diameter this force can amount to 8000 N. For reasons of dimensions, bolted connections can only make use of bolts which are not able to withstand the tensile forces produced at high frequencies. Where form-fitting contact between ceramic and flange is used along with an adhesive, the force that can be transferred from the steel to the ceramic is below the tensile loading level that arises when operating in the high frequency range. Also state-of-the-art shrink-fit locking is not able to withstand the above mentioned loading. The performance of machines with ceramic pistons is therefore markedly limited by the quality of the metal-ceramic connection.
If the connection is weakened, for example by a screw breaking, the ceramic piston is immediately released and damages the piston housing to such an extent that the pumping facility is no longer usable.
In view of the foregoing it is the object of the present invention to develop a process for shrink-fit locking a cylindrical, in particular a ceramic piston in a steel holder connected to a drive in a facility for conveying fluid or gaseous media, by introducing part of the ceramic component into a bore in a heated flange and cooling the same to room temperature, by which process a metal-ceramic connection is assured that does not exhibit the previously mentioned disadvantages; in particular, in the case of piston diameters of typically 20-30 mm the aim is to produce connections which are capable of withstanding forces of 4000 N per cm.sup.2 of ceramic-metal contact area, acting in the direction of the central axis of the piston.